Throughout this application various publications are referred to in parenthesis. Full citations for these references may be found at the end of the specification immediately preceding the claims. The disclosures of these publications are hereby incorporated by reference in their entireties into the subject application to more fully describe the art to which the subject application pertains.
Subjects with poorly functioning hearts can have compromised blood supply to vital organs. The pumping action of the heart and the systemic blood supply can be improved by the use of an intra-aortic balloon pump (IABP) to control an intra-aortic balloon (IAB). IABPs are used in cardiology patients and cardiac surgery patients (Baskett et al., 2002; Mehlhorn et al., 1999).
In each cardiac cycle, the LAB is inflated by means of the pumping device after the end of the ejection phase of the left ventricle of the heart, and is deflated again before the commencement of the following ejection phase. It has been suggested that systemic hemodynamics and myocardial efficiency can be improved by balloon deflation approaching or simultaneous with left ventricular ejection (Kern et al., 1999). For optimal functioning of the IABP, it is important that the IAB be inflated and deflated at the correct times in the cardiac cycle.
Methods and apparatus for controlling the inflation of an LAB have been described, for example, in Sakamoto et al., 1995; U.S. Pat. Nos. 4,692,148, 6,258,035, 6,569,103 and 6,887,206; and U.S. patent application Publication Nos. 20040059183 and 20050148812.
Deflation of the IAB can be triggered using the electrocardiogram (ECG) of the subject's heart (e.g., Ohley et al., 2002; U.S. Pat. Nos. 4,692,148, 4,809,681, 6,290,641 and 6,679,829). Methods and apparatus for determining a trigger signal from an ECG have been described (e.g., U.S. Pat. Nos. 4,571,547 and 5,355,891). Typically, the timing of deflation of the IAB is based on the R Wave of the ECG. There is a need for accurate R wave triggering where the trigger adapts in real time to changes in R wave amplitude and rise time during the leading phase of the R wave.